The Effect of Bladder and Rectum Volume Changes on Exposed Organ Volume During Intensity-Modulated Radiotherapy for...

This retrospective cohort study aims to study the changes of the exposed volume of the bladder and rectum under different filling states, and to clarify the influences of the morphing organs on themselves and each other, to provide the basis for reducing the risk of organ damage by intensity-modulated radiotherapy (IMRT) for cervical cancer.

A retrospective analysis was performed on 24 patients with cervical cancer who received IMRT. Before radiotherapy, a comfortably full bladder and active defecation was ensured for all patients, and interative cone-beam computed tomography (iCBCT) was performed to delineate the bladder, rectum, and small intestine. The filling degree of the bladder, rectum, and small intestine and their intersection with the planned target volume were recorded.

83.44% of patients exhibited reduced bladder volume during treatment. When the planned bladder volume was 400-500 cc, the bladder volume changed the least during treatment (F = 58.39, P < .001). The exposed volume of the small intestine was moderately correlated with the degree of bladder filling (r = -.674, P < .01). For every 10% increase in bladder volume, the exposed volume of the small intestine decreased by 24.05% (P < .01). Furthermore, 45.83% patients had an increase in rectum volume during treatment. The exposed volume increased by 9.47% for every 10% increase in rectum volume (P < .01).

Comfortable bladder and active defecation regimens may not keep bladder and rectal stability. Targeting a planned bladder volume of 400 to 500cc minimizes intrafraction variability. Strategic bladder filling optimization may mitigate small intestine exposure.